The following processes are known for preparing quinazolin-4-one or its derivatives from anthranilic acid or its derivatives.
1) EP 1029853 discloses a process for preparing 6-iodoquinazolin-4-one by reacting 5-iodoanthranilic acid with formamidine acetate in ethanol for 20 hours. This process has problems in that the reaction period is long, and it is necessary to use expensive formamidine in an excessive amount.
2) Chem. Pharm. Bull., 46, 1926 (1998) describes a process for preparing quinazolin-4-one by reacting anthranilic acid with formamide. This process has a problem in that teratogenetic formamide is used in an excessive amount.
Thus, these processes have various problems, and hence are not satisfactory as industrially employable processes for preparing quinazolin-4-one or its derivatives.